This invention relates generally to vision systems for vehicles and, more particularly, to rearview vision systems which provide the vehicle operator with scenic information in the direction rearward of the vehicle. More particularly, the invention relates to a rearview vision system utilizing image capture devices, such as CMOS imaging arrays and the like.
A long-felt need in the art of vehicle rearview vision systems is to reduce the amount of time spent gathering information of the condition around the vehicle in order to safely carry out a vehicle maneuver such as a turn or a lane change. It has been determined that up to about 50 percent of maneuver time is spent gathering information with conventional rearview mirrors. This typically requires viewing one or more mirrors, turning the head and body to check blind spots, and double-checking the mirrors prior to executing the maneuver. Some improvement has been obtained by adjusting mirror optics, for example, to increase the observed field of view rearward of the vehicle. However, this is achieved with an increase in image distortion which makes driver awareness of conditions to the side and rear of the vehicle even more difficult.
Another long-felt need in the art of vehicle rearview vision systems has been to eliminate exterior rearview mirrors by utilizing image capture devices, such as cameras, in combination with dashboard displays. This would be beneficial because it would reduce wind drag on the vehicle, wind noise and vehicle weight. Furthermore, rearview mirrors protrude a substantial distance from the side of the vehicle, which makes maneuvering in tight spaces more difficult. Image capture devices are capable of positioning in a greater variety of locations on the vehicle, providing more flexibility of vehicle styling. It is further expected that camera systems would greatly reduce the blind spots to the sides and rear of the vehicle common with vehicles equipped with conventional rearview mirror systems. The driver cannot perceive vehicles, objects, or other road users in such blind spots without turning his or her body, which interferes with forward-looking visual activities.
Camera-based rearview vision systems for vehicles have not obtained commercial acceptance. One difficulty with proposed systems has been that they present a large amount of visual information in a manner which is difficult to comprehend. This difficulty arises from many factors. In order to significantly reduce blind spots, multiple image capture devices are typically positioned at various locations on the vehicle. The image of an object behind the equipped vehicle is usually captured by more than one image capture device at a time and displayed in multiple images. This may confuse the driver as to whether more than one object is present. When multiple image capture devices are positioned at different longitudinal locations on the vehicle, objects behind the vehicle are at different distances from the image capture devices. This results in different image sizes for the same object. This effect is especially noticeable for laterally extending images, such as a bridge, highway crosswalk markings, the earth""s horizon, and the like. Such images are at different vertical angles with respect to the image capture devices. This results in different vertical positions on the display causing the elongated image to appear disjointed.
A camera system provides a monocular view of the scene, compared to the binocular stereoscopic view obtained when the scene is viewed through a rearview mirror. This makes the ability to judge distances in a camera system a problem. This effect is most noticeable at distances close to the vehicle where stereoscopic imaging is relied upon extensively by the driver in judging relative locations of objects. Therefore, known camera systems fail to provide to the driver important information where that information is most neededxe2x80x94at small separation distances from surrounding objects.
Another difficulty with camera systems is that, in order to provide a sufficient amount of information, the camera system typically presents the driver with a greatly increased field of view. This improves performance by further reducing blind spots at the side and rear of the vehicle. However, an increased field of view is often obtained by utilizing a wide-angle lens which introduces distortion of the scene and further impairs the ability of the driver to judge distances of objects displayed. The problem with such distortion of the scene is that the driver must concentrate more on the display and take a longer time to interpret and extract the necessary information. This further distracts the driver from the primary visual task of maintaining awareness of vehicles and other objects in the vicinity of the driven vehicle.
Yet an additional difficulty with camera systems is that flat panel displays present the image captured by the rearward-facing image capture device, or devices, at a focal length that approximates the arm length of the vehicle driver. In order to observe the condition of the vehicle utilizing the rearview vision system, the driver must change his or her gaze from the forward field of view of the vehicle to the display. Because the forward field of view of the vehicle is at a focal length that is much greater than the focal length of the displayed image, the eyes of the driver must refocus upon changing gaze. This refocusing further increases the amount of time for the driver to assimilate the information in the displayed image. Furthermore, when the gaze of the driver returns to the forward field of view, the eyes must, again, refocus to the greatly longer distance.
Yet an additional difficulty with camera systems is that of finding adequate space in the crowded area of the vehicle""s dashboard for the components making up the display.
The present invention is directed towards enhancing the interpretation of visual information in a rearview vision system by presenting information in a manner which does not require significant concentration of the driver or present distractions to the driver. This is accomplished according to an aspect of the invention in a rearview vision system having at least two image capture devices positioned on the vehicle and directed generally rearwardly with respect to the direction of travel of the vehicle. A display is provided for images captured by the image capture devices. The display displays an image synthesized from outputs of the image capture devices which approximates a rearward-facing view from a single location. In order to obtain all of the necessary information of activity, not only behind but also along side of the vehicle, the virtual camera should be positioned forward of the driver. The image synthesized from the multiple image capture devices may have a dead space which corresponds with the area occupied by the vehicle. This dead space is useable by the driver""s sense of perspective in judging the location of vehicles behind and along side of the equipped vehicle.
The present invention provides techniques for synthesizing images captured by individual, spatially separated, image capture devices into such ideal image, displayed on the display device. This may be accomplished, according to an aspect of the invention, by providing at least three image capture devices. At least two of the image capture devices are side image capture devices mounted on opposite sides of the vehicle. At least one of the image capture devices is a center image capture device mounted laterally between the side image capture devices. A display system displays an image synthesized from outputs of the image capture devices. The displayed image includes an image portion from each of the image capture devices. The image portion from the center image capture device is vertically compressed.
It has been discovered that such vertical compression substantially eliminates distortion resulting from the spatial separation between the cameras and can be readily accomplished. In an illustrated embodiment, the image compression is carried out by removing selective ones of the scan lines making up the image portion. A greater number of lines are removed further away from the vertical center of the image.
The compression of the central image portion produces a dead space in the displayed image which may be made to correspond with the area that would be occupied by the vehicle in the view from the single virtual camera. Preferably, perspective lines are included at lateral edges of the dead space which are aligned with the direction of travel of the vehicle and, therefore, appear in parallel with lane markings. This provides visual clues to the driver""s sense of perspective in order to assist in judging distances of objects around the vehicle.
According to another aspect of the invention, image enhancement means are provided for enhancing the displayed image. Such means may be in the form of graphic overlays superimposed on the displayed image. Such graphic overlap may include indicia of the anticipated path of travel of the vehicle which is useful in assisting the driver in guiding the vehicle in reverse directions. Such graphic overlay may include a distance grid indicating distances behind the vehicle of objects juxtaposed with the grid.
According to yet an additional aspect of the invention, a rearview vision system for a vehicle includes at least one image capture device positioned on the vehicle and directed generally rearwardly with respect to the direction of travel of the vehicle. A display system is provided which displays a rear image synthesized from an output of the image capture device. The rear image is substantially contiguous with the forward field of view of the vehicle driver and at a focal length that is forward of the vehicle passenger compartment and preferably within the depth of field of a vehicle driver viewing a distant object. Because the image has a focal length that more closely matches that of the forward field of view observed by the driver, the need for the driver""s eyes to refocus from the forward field of view to a much shorter focus distance each time the gaze of the driver is directed at the display system is minimized. This reduces the amount of time required for the driver to gaze at the displayed image and interpret objects displayed in the image. Furthermore, the reduction in the repeated refocusing of the driver""s eyes reduces driver fatigue. If there are any near field objects in the periphery of the driver""s forward field of view, such as windshield wipers, windshield frame, dashboard, and the like, the display system is preferably positioned in a manner which blocks the view of such near field objects. In this manner, the driver""s gaze may shift between the forward field of view and the long focal length display system without being refocused on the near field objects. This is based upon a recognition that the driver""s eyes will tend to refocus on the near field object momentarily even though the gaze is being redirected between the forward field of view and the display system.
According to yet an additional aspect of the invention, a rearview vision system for a vehicle includes at least one image capture device positioned on the vehicle and directed generally rearwardly with respect to the direction of travel of the vehicle. A display system is provided for displaying a rear image captured by the image capture device. The displayed image is a unitary image having an aspect ratio that is between approximately 4:1 and approximately 2:1. In a most preferred embodiment, the image has an aspect ratio that is approximately 8:3. The aspect ratio, according to this aspect of the invention, is especially useful where the unitary image is synthesized from a plurality of images which are captured by a plurality of image captured devices and are tiled by the display device.
According to yet an additional aspect of the invention, a rearview vision system for a vehicle includes a plurality of image capture devices positioned on the vehicle and directed generally rearwardly with respect to the direction of travel of the vehicle. A display system which includes at least one image generator and an optical correction system is provided which displays an image synthesized from outputs of the image capture devices as a unitary image. Alternatively, the display system may include a plurality of image generators, each associated with one or more of the image capture devices and an optical correction system which amplifies images generated by the image generators and merges them into a unitary image. The optical correction system additionally increases the focal length, or lengths, of the image, or images, generated by the image generator, or generators. The display system may be an opaque projection display which is positioned approximately at the driver""s arm length in front of the driver. Alternatively, the display system may be a view-through heads-up display which projects the unitary image onto a combiner in order to combine the unitary image with the forward field of view of the driver.
These and other objects, advantages, and features of this invention will become apparent by review of the following specification in conjunction with the drawings.